( i'm not talking about the nanotech wich are another category of LiPO... but most about the normal lipo... 15C, 20C and 25C)

That person explained me that normally he leave his ebike indoor during winter but that time he visited some friends at 30km from his home with his ebike, he left his ebike outdoor that time.

When he wanted to return home and started using his ebike he observed a big voltage sag and very poor performances. He also observed voltage drop down to 87V with a 24s pack but hi still ahd enough Ah left in the pack.

For him, it was like his pack have a big voltage sag eventhough it have enough Ah left.

In fact the Internal resistance of lipo are excellent in warm temperature, but that change alot with cold temperature!

Unlike LiFePO4, lipo are more affected by cold temp.

LiFePO4 cells have better performances and tolerance with with cold temperature ( i mean under freezing point)

You must remember to let your lipo warm enough before using them or charging them.

In fact it is NOT the capacity that decrease with lithium cells.. it is internal resistance that increase, making more heat lost during discharge.

They are flexible resistive heating elements potted in a silicone sheet you can wrap around anything, or snake one through your pack while building it etc.

If you wanted to get fancy-pants, control it with a brushed motor controller that takes throttle input from a temp sensor in the pack, and gets it's power from the charger so it doesn't train pack power, but always leaves your pack at the regulated temp you want while charging.

The Tesla Roadster has a system on it that won't enable the charger to activate until pack heaters get the temp to a certain minimum point.

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Doctorbass wrote:Unlike LiFePO4, lipo are more affected by cold temp.
LiFePO4 cells have better performances and tolerance with with cold temperature ( i mean under freezing point)

Even LiFePO cells are severely affected by cold. About half way down the first post in my A123 testing thread http://endless-sphere.com/forums/viewto ... ts#p301558 is plots of cell voltage under load of a cell removed from a 5 degrees F freezer. You can see the voltage drop recover as the cell self-heats during discharge.

this work great but don't forget the battery because i forget mine and the voltage was at 2.7 volt !!!for all the cells!! but because it was a a low current draw the battery recover is capacity after 2 recharge

Doctorbass wrote:Unlike LiFePO4, lipo are more affected by cold temp.
LiFePO4 cells have better performances and tolerance with with cold temperature ( i mean under freezing point)

Even LiFePO cells are severely affected by cold. About half way down the first post in my A123 testing thread http://endless-sphere.com/forums/viewto ... ts#p301558 is plots of cell voltage under load of a cell removed from a 5 degrees F freezer. You can see the voltage drop recover as the cell self-heats during discharge.

It is common for any cell to see this reaction with self heating effect on the voltage rise.

I still wonder if there is any chemical damage during the low temp discharge condition during the internal resistance decrease.

According to some specs of A123 system, at low temp their cells have the SOA LVC lowered ( under 2.0V). On the opposite, during charging, their recommanded HVC is higher. ( above 3.6V)

dogman wrote:Reptile heaters would be a great way to warm a pack while parked. Once warm, some insulation should do ok for the ride.

of what i see at -15 I need to use the heater all the time i ride , so for my need I use 1 ah of the lipo pack to power up my heated blanket, but just to be sure
i have plenty of capacity i bring another lipo pack in my pocket , next thing i want to do is to use a tool box for my batteries so i can remove from the bike for charging ,i will also integrate the charger inside the box maybe , i plan to do this once i find a system i can remove in fews second any idea?

Doctorbass wrote:It is common for any cell to see this reaction with self heating effect on the voltage rise.

I still wonder if there is any chemical damage during the low temp discharge condition during the internal resistance decrease.

A123 cells are speced to operate over a pretty wide temperature range. Still, operating them when hot or cold can't possibly be a good thing.

A123 cells have very low internal resistance (and self heating) for LiFePO cells. Still check my testing thread. At 5C discharge they have a 23F open air temp rise. At 7C it is +40F. Cell temp rise is quite a bit more when enclosed. But, at 5C-7C discharge, by the time cell fully warms up, it is almost drained. I would recommend using an externally powered pack heater in cold weather. I don't think that powering the heater off the pack is a winning proposition, particularly with smaller and poorly insulated packs.

Good topic doc & thoughtful inputs. Chemical hand warmer pacs will work, same as charcoal pocket ones. A wind proof outer layer with an inch of quilted fabric will slow cooling by hours at -10c, not very convenient. A foam insulation contractor can make a 2-3 pc. mold cheap, take in the rack & pack. Tape on the heat pads, tape the mold seams, 6-10 hours. Everyones figures match graphs for lifepo4 a123systems, storage is 10 years at -50c, Thermal runaway 800c. I'm in...

A person can purchase a "Battery warmer blanket" from an auto parts store,they are fairly cheap.They will keeps your batteries plenty warm when your bike is parked.Then you could insulate your pack some,and maybe leave some room to slide a couple of those chemical pocket warmers in,or wire in some electric socks or something like that for when you are riding,

Hey Lifepo4ever, your in the lead for proven electric heating know how. Russian members sure got savvy too, gonna learn more. An international community means "whole earth" patent / knowledge access. My opinion is heat any chemistry if its outside for longer than 2 hours at 0 deree C (bats in a plastic case). Lifepo4 appears to work on medium powered bikes to 80% dod at 0.0C temp. You can slow the cooling with insulation schemes...pink glass batts with a plastic wrap will work...what an itchin' mess. Start with air flow barriers, thats what you are doing with flexable plastic foam materials, the R factor is very low for thermal conduction barrier. Rigid foams with small air cells like home depot pink or blue sheets are practical to work with for cutting box dimension cases. Don't get suckered with gas filled R values...they outgas real soon. Rigid & low expansion spray foams are all about the same R, 2" has meaning. If you are heating, get the facts for your brand & its chemistry. A123systems stats has +40C impacting AH, I think the site lists cutoff at +60C. So a trial & error or a mathematic thermal design approach? Oak Ridge National Labratories is a good primer for sorting out insulation manufacturers claims with science backed facts, see : "whole wall" research topics. Watch out for engineering reports using lightbulb heat source, this is mostly insulating paint scams...ain't scam if talking steam temps or certian infared frequencies. Check the cutoff for auto battery wrap temps, used to be +4F, thats too cold, but of some worth & can be altered...MAYBE. Persons having to commute all winter should find a solution with cast foam covers and the correct BTU heating device &values.

Or like I was saying on another topic here,you could purchase a Skidoo "Heated Handgrip Kit",it comes with 2 stick-on heating pads and an off/low/high switch. Fairly compact and cheap,simple to wire in,but you need 12v to run them,if you have a decent DC-DC 12v converter(I've found a few nice ones,10a-15a output). If you then attach some sort of temp. sensor on the pack with a remote temp. gauge you can see then you could flip the warmers on periodically when needed.
Yes I know this will use some battery power up but in cold weather a frozen battery pack is worse I think...

slowlane wrote:Hey Lifepo4ever, your in the lead for proven electric heating know how. Russian members sure got savvy too, gonna learn more. An international community means "whole earth" patent / knowledge access. My opinion is heat any chemistry if its outside for longer than 2 hours at 0 deree C (bats in a plastic case). Lifepo4 appears to work on medium powered bikes to 80% dod at 0.0C temp. You can slow the cooling with insulation schemes...pink glass batts with a plastic wrap will work...what an itchin' mess. Start with air flow barriers, thats what you are doing with flexable plastic foam materials, the R factor is very low for thermal conduction barrier. Rigid foams with small air cells like home depot pink or blue sheets are practical to work with for cutting box dimension cases. Don't get suckered with gas filled R values...they outgas real soon. Rigid & low expansion spray foams are all about the same R, 2" has meaning. If you are heating, get the facts for your brand & its chemistry. A123systems stats has +40C impacting AH, I think the site lists cutoff at +60C. So a trial & error or a mathematic thermal design approach? Oak Ridge National Labratories is a good primer for sorting out insulation manufacturers claims with science backed facts, see : "whole wall" research topics. Watch out for engineering reports using lightbulb heat source, this is mostly insulating paint scams...ain't scam if talking steam temps or certian infared frequencies. Check the cutoff for auto battery wrap temps, used to be +4F, thats too cold, but of some worth & can be altered...MAYBE. Persons having to commute all winter should find a solution with cast foam covers and the correct BTU heating device &values.

the reason i use car seat heater because its just enought to keep the battery warm and very simple to use with a 4s lipo and with the dc/dc converter from lyen i can reduce the voltage output to save some energy i think tomorow i will try it with a 10v ouput ,
the first barrier is the plastic box that cut the windchill , inside the box i will use
foam for the wall , on the bottom of the case i use the seat heater so the heat will keep the 2 lunch bag with insulation(each lunch bag is 50v 10ah) in the good temperature range . my first idea was to use 2 heater but i will need 2 battery to have the same capacity of power so one big heater warm all the box instead

i really like my set up because i can remove the to bag in 30 second to bring inside a house for charging in a warm climate i will post another video soon

I got some of these for christmas to my sister a few years ago, they are re-usable !!

You microwave them or boil them in water and it turns to liquid.. and ready for use.. when you want to use them you snap the metal disk inside and it starts a reaction turning it to crystals that get hot and they store a fair amount of heat..... in an insualted box i'm sure they would do quite well...

There is a good selection of reusable sodium acetate heating pacs available, some very low cost solutions . Steady heat at 130F, 30 minutes to 2 hours, many years of use. There is homemade process at instructables website & others. Stove top method using vinegar & baking soda, non-toxic, claims 100 cycles in an open air container, 1 hour of heating. Large medical pacs available but over priced.

it'S equal to 2.5 ohm... and at 12V coming from a dc-dc it would be 4.8A and around 60Watts of heat power.

If you cover the wires with a little blanket and foil, that would make a battery electric blanket for cheap.

I guess that 60W plus a 35 celsius thermal switch installed on teh battery would be perfect at temp down to -20...

60W is 60Wh consumption during one hour of ebike outdoor wich seem resonnable consumption compared to the problem that could occur with a battery at -20 celsius!

Doc

hey doc in my video i show the heat seat i purchase at the canadian tire this week you can buy one for 5$ and they only need 25 watts and 1.5 amp of current

at -10 my box inside temperature is 11 degree so you don't need more , in a lunch bag its to hot i just bought another thermometer for the bag so when its to cold i start the switch , also my bag are now removable from my box i can carry them inside i will post another video soon